An ingenious example of the product-situation cycle could once be found in a Quebec waterfront hotel called L’Hotel Louis XIV, lamentably destroyed by fire in the 1980s. At the Louis XIV, the term “private bath” meant what it means in many European hotels: the bath is yours but not yours alone, for it is also the private bath of the guest on the other side of the bathroom. This creates a problem. If the bathroom has no inside locks, you have no privacy. But if the doors can be locked from the inside, one forgetful guest can lock the other out indefinitely and almost surely will.

The hotel’s solution, Caplan reveals, was to tie a leather thong to the knob of each door. A guest who wanted to use the bathroom simply hooked the two ends together, stretching them across the room and holding both doors shut. As Caplan notes: “There was no way to get back into your own room without it at the same time unlocking the door for the other guest. It was memorable as the total integration of object and circumstance.”

This is the kind of story I love, so I threw together a post based on Petroski’s version, put it on the blog, and moved on. I couldn’t have spent more than an hour on it, but it got a favorable response from readers that morning, which is all it was ever supposed to do. Earlier this week, however, something unusual happened. I noticed an uptick in views for that page, which occasionally happens when somebody links to one of my old posts online. (This occurs a few times a year with my writeup on Blinn’s Law, which is another throwaway post that took on a life of its own.) It apparently began on Reddit, where a commenter linked to it in a thread for an unrelated story about sharing a bathroom with a sibling. Somebody else evidently posted the same link to Hacker News, the aggregator site associated with the startup incubator Y Combinator. From there, it took off. When I went to bed that night, it was the top post on the front page, and although it soon dropped a few notches, it had a surprising amount of staying power. It was widely shared on Twitter and Facebook, mostly from users who repost anything that gets a lot of upvotes, and it continued to snowball from there. As I write these words, it has over fifty thousand views, which is good enough to make it the second most popular post that I’ve ever published here, topped only by a piece about George R.R. Martin that will probably remain the most widely read thing I’ll ever write, thanks to a similar confluence of factors on social media. Whenever this happens, it fills me with both excitement and anxiety—you just never know where it might lead—but in both cases, I emerged mostly unscathed. There were a few nitpicky comments, but for the most part, people seem to have genuinely liked it.

So why did it catch on? Unlike Caplan and Petroski, who treat the anecdote as a straightforward case study, I framed it as a puzzle, which evidently appeals to the sort of crowd that you find hanging out on Hacker News. This wasn’t a conscious choice, but a result of the way in which I tend to write these posts, and it had a lot to do with the illustration. In The Evolution of Useful Things, Petroski reproduces a line drawing from Caplan’s book, which only shows the bathroom with the solution in place. Since I like to include two pictures with every post, it occurred to me to include a before and after shot. I quickly edited the picture in Seashore to remove the leather strap, and you can still see the traces of my hasty retouching. But the result was a post that looked sort of like one of those visual brainteasers that most of us read growing up, and I think that contributed to its appeal. (Looking back at it now, I see that the original picture in By Design was drawn expressly for the book by the legendary graphic designer Milton Glaser, who is apparently good friends with Caplan. Amusingly, the illustration is the one aspect of the post that generated any criticism, with one commenter complaining: “It’s a poor drawing. They look like doors that open inward. Doors that open outward would be need to be set more deeply into the door frame.”) As a result, it came across as an exercise for the reader, and the ensuing discussion was less about the actual solution at the Hotel Louis XIV and more about various approaches to the problem itself, which I don’t think would have happened if I had written it up as Caplan and Petroski did. This was purely by accident, but it’s interesting, at least to me.

And the thread that it inspired is worth reading. Among other things, it led to a number of useful critiques that had never occurred to me. (One commenter noted that such an arrangement would be hard to open from the outside in case of an emergency, although I think that this problem is more apparent than real. I don’t know what the exact setup was at the hotel, but the term “leather thong” suggests something roughly the thickness of a shoelace, which would present enough resistance to a casual tug to ensure short-term privacy, but would break at a sustained pull. Another reader asked how guests in one room could be prevented from entering the other, and the answer appears in a line from Petroski that I neglected to quote: “Each bathroom door did have a lock on the guest room side, of course, for otherwise a stranger could come in through the common bathroom, but there were no locks at all on the insides of the bathroom doors.”) Other replies were less useful, with some proposing solutions along the lines of motion sensors—“Tech is cool”—or raising persnickety objections: “What if the high humidity of the bathroom causes the leather strap to break at an inopportune time? What happens if the strap gets misplaced or stolen? This is not a good idea.” As the top comment put it:

I’m reminded of a discussion we had here a few weeks ago, where somebody noted that humanity wouldn’t be able to invent, for example, a machine to automatically rack pins at a bowling alley today. The 2018 solution to that problem would automatically involve computer vision, AI and robotics…You can see it happening in some of the comments here.

But there was also a lot of ingenuity and civilized discussion, which pleased me. This was mostly due to the power of the original example, but I think the way that I inadvertently structured the post—which encouraged speculation—had something to do with it, too. It may not quite qualify as “the total integration of object and circumstance.” But it wasn’t bad, either.

Before it was destroyed by fire, L’Hotel Louis XIV, which was located on the waterfront in Quebec, advertised private baths. However, their privacy was of a limited and precarious kind, for each bath was located between a pair of guest rooms, both of which opened into it. This arrangement is not uncommon in private homes, where bedrooms share a bathroom or where a bathroom opening onto a bedroom also opens into a hallway. In all such situations, the basic design objective is to achieve privacy for whoever might be using the bathroom. This can be achieved in many ways, of course, and the most obvious and common way is to have locks on each of the doors, so that the bathroom user may bar others from entering. The failure of this solution is frequent and frustrating: the person who has finished with the bathroom forgets to unlock the second door, causing at least a little inconvenience for the next user who tries to enter it. In bathrooms shared by siblings, screaming through the locked door may or may not get results, but generally there is little more than the temporary inconvenience of having to go around to the other door or to another bathroom in the house. Families that find bathroom doors too frequently locked can remove all locks from the doors and trust everyone to knock before entering.

“In the case of bathrooms shared by unrelated guests,” Petroski continues, “the problem is less easily solved.” Consider, for example, the hotel bathroom shown above. There are two doors, each opening into a separate room occupied by a guest who is presumably a stranger to the other. You need locks on both doors to ensure privacy for each occupant, which means that you’ll invariably wind up with situations in which one guest leaves and forgets to unlock the second door, leading to considerable inconvenience. What do you do? You could, of course, tear down and rebuild the entire hotel, at great expense, so that each room has its own bathroom—a solution that might sound ridiculous, but isn’t so far removed from how similar design problems are addressed every day. More plausibly, you could somehow label the doors. Petroski notes that this was the approach employed by a similar house in which he once stayed in St. Louis: “The measures taken to avoid this situation consisted of a nicely printed sign placed prominently on the dresser beside the bathroom door, reminding each guest to unlock the other guest’s door before leaving the bathroom. I am sure I was not the only guest who suffered from the inadequacy of that solution.” Alternatively, if you were of a mechanical disposition, you could rig up an alarm system that would sound a buzzer if one door was unlocked without the other. This would have obvious shortcomings in practice, and it would also annoy guests who just wanted to use the bathroom in peace.

In the end, the proprietors of the Hotel Louis XIV came up with an ingenious answer, as outlined in the book By Design by Ralph Caplan, which was Petroski’s source for the original case study:

Well, there were no locks on the bathroom doors of the Louis XIV, but tied to each doorknob was a three-and-a-half foot length of leather thong to which a hook was attached. When you were in the bathroom you simply linked the two hooks together, holding both doors shut. There was no way to get back into your own room without it at the same time unlocking the door for the other guest. It was memorable as the total integration of object and circumstance.

It’s a lovely solution—so much so, in fact, that Caplan’s book puts it into its own subtitle: Why There Are No Locks on the Bathroom Doors in the Hotel Louis XIV. And at the heart of the answer lies a subtle change in the way the problem is understood. Other measures, like putting up a sign, focused on the idea that both doors had to have locks, when the lock is really just an interim solution to the underlying problem, rather than the problem itself. As Petroski puts it: “The basic design objective is to achieve privacy for whoever might be using the bathroom.” And once the problem is phrased in such a way as to leave locks out of the equation entirely, you’re that much closer to figuring out how to address it.

And it’s a lesson that writers or other creative artists should take to heart. In On Directing Film, David Mamet devotes what seems like an inordinate amount of time to teaching his students how to properly describe the objective of a scene, and reminding them how easy it is to confuse the means with the end. One of the pitfalls of figuring out a plot is that once we’ve come up with a “solution” to a problem, like putting locks on the doors, we spend all our energy trying to get out of all the new complications that the solution presents, rather than focusing on the issue that it was meant to satisfy. In many cases, like the proprietors of the rooming house in St. Louis, we end up affixing a label to explain what we mean, which is as close as you can get to unambiguous evidence that the solution you have in mind isn’t working. Donald Norman, in his classic book The Design of Everyday Things, provides examples of the labels we see on everything from doors to to hot and cold water faucets, and concludes: “When simple things need instructions, it is a certain sign of poor design.” And that’s as true of stories as of sinks. Whenever a movie gives us an introductory scroll of text, a lingering shot of a sign, or a chyron to explain where we are or how much time has passed, it signals that the underlying problem hasn’t really been solved. If you want to find the right answer, you have to start by asking the right question. And then you can soak in the tub until you’ve figured it out—as long as you remember to lock the door first.